Free-wheel with a free-wheel outer rim covered with fiber-reinforced plastic

ABSTRACT

The invention relates to a free-wheel, in particular a pinch roller free-wheel or a pinch body free-wheel, comprising relatively-rotating elements arranged one within the other on a common axis, which form a gap, in which pinch elements, in particular pinch rollers or pinch bodies, are arranged such that a friction connection can be produced with the facing outer surfaces of the elements, by means of the pinch surfaces, whereby the free-wheel outer rim is covered by a ring of fibre-reinforced plastic and the external diameter of the ring of fibre-reinforced plastic is about 1.3 to 1.8 times the diameter of the external clamping surface.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. 119 of German PatentApplication No. 101 44 032.4 filed Sep. 7, 2001. Applicant also claimspriority under 35 U.S.C. §365 of PCT/DE02/03161 filed Aug. 28, 2002. Theinternational application under PCT article 21 (2) was not published inEnglish.

The invention relates to a free-wheel, in particular a pinch rollerfree-wheel or a pinch body free-wheel having elements which can rotatewith respect to one another about a common axis, are arranged one insidethe other and form a gap in which pinch elements, in particular pinchrollers or pinch bodies are arranged in such a way that a frictionallylocking connection can be brought about with the facing outer surfacesof the elements, in particular pinch rollers or pinch bodies arearranged in such a way that a frictionally locking connection cab bebrought about with the facing outer surfaces of the elements by means ofthe clamping surfaces.

Clamping free-wheels are components which are frequently used intechnology. They are used primarily as a directional clutch oroverrunning clutch, a reversing lock and a gear-shifting free-wheel. Thetorque which can be transmitted by a free-wheel depends decisively onthe design of the shaft and of the outer ring of the free-wheel. Thetorque which can be transmitted is often limited by the widening of thegap between the shaft and the outer ring of the free-wheel. Reducing thewidening of the outer ring of the free-wheel can thus lead to anincrease in the torque of the free-wheel.

The invention is based on the object of providing a free-wheel in whichundesired widening of the outer ring of the free-wheel is reduced oravoided. The object is achieved by a free-wheel, in particular a pinchroller free-wheel or a pinch body free-wheel having elements which canrotate with respect to one another about a common axis, are arranged oneinside the other and form a gap in which pinch elements, in particularpinch rollers or pinch bodies are arranged in such a way that africtionally locking connection can be brought about with the facingouter surfaces of the elements, in particular pinch rollers or pinchbodies are arranged in such a way that a frictionally locking connectioncab be brought about with the facing outer surfaces of the elements bymeans of the clamping surfaces, wherein a ring made of fiber-reinforcedplastic is wound around the outer ring of the free-wheel and theexternal diameter of the ring made of fiber-reinforced plastic isapproximately 1.3 to 1.8 times the diameter of the external clampingsurface. Advantageous developments of the invention are described below.

In the free-wheel according to the invention, a ring made offiber-reinforced plastic is wound around the outer ring of thefree-wheel. For this purpose, the outer ring of the free-wheel which isin particular cured is additionally wound, after the curing process,with at least one ring made of fiber-reinforced plastic over individualring width regions or the entire width of the ring, or the ring made offiber-reinforced plastic is wound into at least one circumferentialgroove which is formed in the outer ring of the free-wheel before thecuring. It is also possible to provide a plurality of circumferentialgrooves in the outer ring of the free-wheel. The circumferential grooveis to be shaped in such a way here that the cured outer ring of thefree-wheel can be used as a coil former for winding on the ring made offiber-reinforced plastic. The fibers are wound on a winding machine withappropriate prestress.

The position of the fibers is advantageously essentially unidirectionalhere and about one axis in the circumferential direction so that thehigh modulus of elasticity of the fiber is utilized. As a result,widening of the outer ring of the free-wheel is counteracted in anoptimum way owing to the contact force of a pinch body. This results ina higher transmissible torque since the pinch body rolls in less farowing to the smaller degree of widening of a gap between a shaft and theouter ring of the free-wheel, and the permitted compressive load perunit area is, at the same time, used better.

The thickness of the outer ring of the free-wheel and the depth of thecircumferential groove depend here on the torque to be achieved and thesize of the compressive load per unit area between an external clampingface of the pinch body and the outer ring of the free-wheel. Thecompressive surface loading is to be prevented from acting on thewound-on ring made of fiber-reinforced plastic via the outer ring of thefree-wheel.

The height of the ring made of fiber-reinforced plastic should notexceed the depth of the circumferential groove in the outer ring of thefree-wheel. This is ensured by virtue of the fact that fitting surfaces,which can also be arranged between adjacent grooves, permit the outerring of the free-wheel to be introduced into a corresponding housingwithout damaging the fibers. The width of the circumferential groove,and thus of the ring made of fiber-reinforced plastic, canadvantageously be equal to the width of the clamp body or exceed it. Thering made of fiber-reinforced plastic is thus wound in such a way thatthe entire width of the circumferential groove is filled with fibers.

The free-wheel according to the invention has a ring made offiber-reinforced plastic which is constructed so as to be considerablystrengthened in comparison with the outer ring of the free-wheel. Theexternal diameter of the outer ring of the free-wheel is hereapproximately 1.02 to 1.1 times the diameter of the external clampingsurface. Here, the external diameter of the ring made offiber-reinforced plastic is approximately 1.3 to 1.8 times the diameterof the external clamping surface of the free-wheel according to theinvention. This produces a free-wheel with an outer ring free-wheelcovering which is embodied in a filigree fashion in comparison with thering made of fiber-reinforced plastic. The combination of an outer ringof a free-wheel which is of such thin design with a ring made offiber-reinforced plastic which is reinforced in this way has provenparticularly resistant to loading and durable during vibration testing.

The object can be used in order to counteract the radial widening ofsteel rings owing to internal loading such as internal pressure,compressive surface loading or contact forces. The additional reductionin mass makes it possible to apply the invention also to rings whichrotate at high speed and are thus dynamically loaded.

The embodiment according to the invention will be explained in moredetail below with reference to exemplary embodiments, in which:

FIG. 1 shows a schematic sectional view in the circumferential directionof a free-wheel,

FIG. 2 shows a first sectional view, extending in the axial direction,of the wound outer ring of a free-wheel according to FIG. 1,

FIG. 3 shows a further sectional view, extending in the axial direction,of a wound outer ring of a free-wheel according to FIG. 1 with thegroove formed,

FIG. 4 shows a schematic sectional view in the circumferential directionof a free-wheel with a housing, and

FIG. 5 shows a sectional view of a free-wheel according to FIG. 4, whichextends in the axial direction.

The free-wheel is composed of a shaft 1 (or of a free-wheel inner ringwhich is known per se and is not illustrated) and an outer ring 3 of thefree-wheel (of which a portion is illustrated), said inner ring andouter ring 3 of the free-wheel being rotatable with respect to oneanother about a common axis 2 and being arranged one in the other, andthus forming a gap 4. For example three pinch bodies 5, which have, inthe radial direction, an internal clamping surface 6 and an externalclamping surface 7 which are applied to the shaft 1 and to the outerring 3 of the free-wheel and thus form a functionally lockingconnection, are arranged in this gap 4.

In order to secure them positionally, the pinch bodies 5 are insertedinto a pinch body cage 8 and are additionally secured by a tensionspring 9. The outer ring 3 of the free-wheel can have, on the externaldiameter, a circumferential groove 11 which is preferably formed beforethe outer ring 3 of the free-wheel is cured. A ring made offiber-reinforced plastic 12 is wound into the circumferential groove 11in order to avoid or reduce widening of the outer ring 3 of thefree-wheel.

The fibers are preferably unidirectional. This ensures a high modulus ofelasticity of the wound ring made of fiber-reinforced plastic 12, whichis higher than the modulus of elasticity of the outer ring 3 of thefree-wheel. This ensures that the widening of the entire outer ring 3 ofthe free-wheel is reduced owing to the contact force of the pinch bodies5. This reduces the angle of rotation between the shaft 1 and the outerring 3 of the free-wheel when a torque is acting, which permits thepinch body 5 also to roll in to a lesser degree. This generally resultsin a higher torque. The lower specific density of the fiber-reinforcedplastic reduces the mass of the outer ring 3 of the free-wheel incomparison with that of a solid steel ring. Correspondingly, use indynamic applications, such as high switching frequencies, is favored.Furthermore, the installation space can be reduced, while maintainingapproximately the same torque, by reducing the external diameter of theouter ring 3 of the free-wheel.

The depth of the circumferential groove 11 must be selected in such away that the effect of the compressive surface loading can be absorbedby the outer ring 3 of the free-wheel made of steel and is nottransferred to the wound ring made of fiber-reinforced plastic 12.

In order to accommodate the outer ring 3 of the free-wheel in acorresponding housing 14, preferably two cylindrical fitting surfaces 13are provided. The height of the wound ring made of fiber-reinforcedplastic 12 does not exceed the height of the fitting surfaces 13 here,in order to avoid damage to the ring made of fiber-reinforced plastic 12when the outer ring 3 of the free-wheel is introduced into the housing14. In addition, it is also possible to provide a plurality of fittingsurfaces 13 between which a plurality of adjacent rings made offiber-reinforced plastic 12 (not illustrated) are inserted.

FIG. 4 and FIG. 5 show a free-wheel whose outer ring 3 is wound with aring made of fiber-reinforced plastic 12 over the entire width of theouter ring. The ring made of fiber-reinforced plastic 12 is then in turnsurrounded by a housing 14.

In all the illustrations of the free-wheel according to the invention inFIGS. 1–5, the geometrical dimensioning, in particular of the ring madeof fiber-reinforced plastic 12 and of the external diameter of the outerring 3 (and of the housing 14), is highly significant for theoperational capability and durability of the free-wheel. According tothe invention, in particular the outer ring 3 of the free-wheel is madesignificantly thinner and narrower than the ring made offiber-reinforced plastic 12, in particular the size relationships thatthe external diameter of the ring is approximately 1.3 to 1.8 times, andthe external diameter of the outer ring of the free-wheel is 1.02 to 1.1times, the diameter—measured from the axis 2—of the external clampingsurface 7 producing particularly advantageous oscillation properties,which are advantageous and discernable during extended testing, alongwith dynamic operating characteristics of the free-wheel.

The wall thickness of the outer ring 3 of the free-wheel can be,depending on the overall size, 1–1.5 mm in order to be able to absorbthe Hertzian stresses occurring during operation. The hardness of theouter ring 3 of the free-wheel may be, in particular, HRC=60+4.

The outer ring 3 of the free-wheel should be pressed into the ring madeof fiber-reinforced plastic 12 with a tight fit. When the elastic partsof the thin-walled steel ring and settling processes which would occurwith a loose fit are thus minimized when loading by the pinch bodies 5occurs. The positive property of the high modulus of elasticity(E-modulus) of the ring made of fiber-reinforced plastic 12 thus becomesimmediately effective when the load is taken up. A fitting pair 7, 6 ofthe ring made of fiber-reinforced plastic 12 and outer ring 3 of thefree-wheel, for example, is thus suitable.

The ring made of fiber-reinforced plastic 12 is wound or manufactured,for example, from UHM GY-70 (E-modulus=290 GPa, that is to say 290×10³N/mm²) (carbon fiber with an ultra high modulus). During manufacture itis necessary to ensure that the fiber is wound in the circumferentialdirection. Basically all UHM materials which have an E-modulus of atleast 210 GPa (that is to say 210×10³ N/mm²) are basically possible.

The ring made of fiber-reinforced plastic 12 cannot be pressed directlyinto other components since here there is the risk of the fiber beingdamaged during the pressing in and the properties of the ring beingadversely affected.

In order to adapt the invention with other components, the ring made offiber-reinforced plastic 12 according to FIG. 3 and FIG. 4 can also besurrounded by a housing 14 (or a further ring, in particular an outerring) which has the function of protecting the ring made offiber-reinforced plastic 12 and also permitting it to be pressed intoother components. The housing 14 should, for reasons of weight, be madewith thin walls and be fabricated from a metallic material (for examplesteel, aluminum wrought alloys etc.). In particular, the wall thicknessof the housing 14 or of the ring can correspond approximately to thewall thickness of the outer ring 3 of the free-wheel (cf. FIG. 4 andFIG. 5).

In one particularly advantageous embodiment, the free-wheel according tothe invention is used as a weight-saving and low-noise pinch bodyfree-wheel for (high performance) motor cycles (in particular for wheelhubs), as a result of which pinch roller free-wheels which have beenused hitherto for reasons of weight and whose noise was tolerated, canbe replaced.

REFERENCE NUMERALS

-   1 Shaft-   2 Axis-   3 Free-wheel outer ring-   4 Gap-   5 Pinch body-   6 Internal clamping surface-   7 External clamping surface-   8 Pinch body cage-   9 Tension spring-   11 Circumferential groove-   12 Ring made of fiber-reinforced plastic-   13 Fitting surfaces-   14 Housing

1. A free-wheel comprising: (a) at least first and second elementsrotatable with respect to each other about a common axis, said elementsbeing arranged one inside the other and forming a gap, each elementhaving an outer surface; (b) a plurality of pinch elements arranged inthe gap, each pinch element having a clamping surface with a diameter,the pinch elements being arranged so that a frictionally lockingconnection is brought about with the outer surfaces of the elements viathe clamping surfaces; (c) a ring made of fiber-reinforced plastic withfibers wound unidirectionally in circumferential direction around anouter ring of one of the elements, said ring having an external diameterapproximately 1.3 to 1.8 times the diameter of one of the externalclamping surfaces; wherein a circumferential groove with side walls ofidentical height into which the ring made of fiber-reinforced plastic iswound is formed in the outer ring.
 2. The free-wheel as claimed in claim1, wherein the outer ring has an external diameter approximately 1.02 to1.1 times the diameter of the external clamping surface.
 3. Thefree-wheel as claimed in claim 1, wherein the modulus of elasticity ofthe fiber-reinforced plastic is higher than the modulus of elasticity ofthe outer ring.
 4. The free-wheel as claimed in claim 3, wherein themodulus of elasticity of the fiber-reinforced plastic exceeds 210 GPa.5. The free-wheel as claimed in claim 1, wherein the outer ring hasfitting surfaces and the height of the ring made of fiber-reinforcedplastic does not exceed the fitting surfaces.
 6. The free-wheel asclaimed in claim 1, wherein the ring made of fiber-reinforced plasticcomprises a plurality of winding layers.
 7. The free-wheel as claimed inclaim 6, wherein the winding layers of the ring made of fiber-reinforcedplastic are arranged essentially unidirectionally in the circumferentialdirection.
 8. The free-wheel according to claim 1 wherein the free wheelis a pinch roller free-wheel or a pinch body free-wheel and the pinchelements are pinch rollers or pinch bodies.